Processes of regenerating chemical nickel plating solutions



United States Patent 1 PROCESSES OF REGENERATING CHEMICAL NICKEL PLATIIJG SOLUTIONS Norma L. Duvall, Lansing, Ill., assignor to General American Transportation Corporation, Chicago, Ill., a cor poration of New York Application January 17, 1958, Serial No. 709,690

11 Claims. (Cl. 106-1) Patent No. 2,717,218, granted on September 6, 1955, to

Paul Talmey and William I. Crehan.

A number of suitable plating solutions are available for the present purpose, as disclosed in U.S. Patent No. 2,532,283, granted on December 5, 1950, to Abner Brenner and Grace E. Riddell; in US. Patent No. 2,65 8,-

841, granted on November 10, 1953, to Gregoire Gutzeit and Abraham Kiieg; and in US. Patent No. 2,658,842, granted on November 10, 1953, toGregoire Gutzeit and Ernest J. Ramirez; as well as in the copending application of Gregoire Gutzeit, Serial No. 376,977, filed August 27, 1953; the copending application of Gregoire Gutzeit, Paul T almey and Warren G. Lee, Serial No. 478,492, filed December 29, 1954; and in the copending application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, Serial No. 569,815, filed March 6, 1956, now US. Patent No. 2,822,294.

A chemical nickel plating solution of this type essentially comprises an aqueous solution of nickel cations and hypophosphite anions, the nickel cations being d rived from nickel sulfate, nickel chloride, nickel hypophosphite, etc., and the hypophosphite anions being derived from hypophosphorous acid, sodium hypophosphite, potassium hypophosphite, nickel hypophosphite, etc. Preferably, such a plating solution comprises an absolute concentration of hypophosphite anions within the range 0.15 to 1.20 moles/liter, a ratio between nickel cations and hypophosphite anions expressed in molar concentrations within the range 0.25 to 1.60, and a pH in the range 4.5 to 11. The plating solution disclosed in the Gutzeit, Talmey and Lee application Serial No. 569,815 is particularly advantageous and comprises, in addition to the nickel cations and the hyphophosphite anions, lactic anions and propionic anions, and having a pH in the acid range 4.4 to 5.6; and specifically this plating bath comprises an absolute concentration of hypop-hosphite anions within the range 0.15 to 1.20 moles/liter, a ratio between nickel cations and hypophosphite anions expressed in molar concentrations within the range 0.25 to 1.60, an absolute concentration of lactic anions within the range 0.25 to 0.60 mole/liter and an absolute concentration of prop-ionic ions within the range of 0.025 to 0.060. A typical plating solution of this type has the following composition:

Nickel ion (as nickel sulfate) m.p.l 0.08 l-Iypophosphite ion (as sodium hypophosphite) m.p.l 0.225 Lactic ion (as lactic acid) m.p.l 0.30 Propionic ion (as propionic acid) m.p.l 0.03 pH (adjusted with H 80 and NaOH) 4.5 to 4.7

In the continuous plating system, as the nickel reduc- W tion-bypophosphite oxidation reaction proceeds, the nickel cations and hypophosphite anions are depleted with the formation of hydrogen ions; and in order to preserve substantially the initial composition of the plating solution, the same is partially regenerated, either periodically or continuously, by the addition of nickel cations, hypophosphite anions and hydroxyl anions; however, as this partial regeneration proceeds, there is a build-up in the plating solution of phosphite anions, the anions of the nickel salt employed and the cations of the hypophosphite employed. Assuming that the plating solution is initially composed, and is regenerated, employing nickel sulfate, sodium hypophosphite and sodium hydroxide, it is apparent that phosphite anions, sulfate anions and sodium cations build-up in the plating solution, as a result of the use and regeneration mentioned.

The build-up of substantial phosphite anions in the plating solution is particularly undesirable, since ultimately nickel phosphite will be precipitated therein, the tolerance of the plating solution to the presence of phosphite anions therein being dependent upon the particular composition of the plating solution, the plating-solution of the composition specified above having a phosphite anion tolerance in excess of about onemolar.

Nevertheless, the presence of the phosphite anions in the plating solution is objectionable, whereby there is disclosed in the copending application of Paul Talmey, Gregoire Gutzeit and Donald E. Metheny, Serial No. 576,931, filed April 9, 1956, a process for completely regenerating such a chemical nickel plating solution involving the removal therefrom of the phosphite anions (as well as the sodium cations and the sulfate anions in the case where the bath is composed and regenerated employing nickel sulfate and sodium hypophosphite), to gether with the additions of nickel cations, hypophosphite anions and hydroxyl ions. This process of Talmey, Gutzeit and Metheny is very advantageous in view of the fact that a regenerated chemical plating solution is brought back substantially to the initial composition thereof with no resulting build-up therein of phosphite anions, and the other ions mentioned. In accor'dance'with the fundamental principle of this process, the depleted chemical nickel plating solution is first contacted by a cation exchange resin, so as to bring about the extraction therefrom of the nickel cations; then the effluent is subjected to calcium hydroxide treatment, wherein the pH of the solution is increased well into the base range bringing about the precipitation of calciumphosphite. The resulting solution is then filtered to remove the precipitated calcium phosphite therein; and the filtrate is cooled to a temperature within the general range 0 C. to 5 C., bringing about the crystallization therein of sodium 'sulfate. This solution is thenfiltered to remove the sodium sulfate therefrom; and the resulting filtrate is reco'nsti tuted by the addition thereto of nickel sulfate, sodium hypophosphite and sulfuric acid.

While this process is entirely satisfactory for the. pur pose of completely regenerating the depletedplating solution, it is subject to the criticism that it involves a larger number of individual steps than are desirable, as it is emphatic in carrying out the process that the nickelcations must be removed from the depleted platingsolution prior to the treatment thereof with calcium hydroxidein the substantial base range, as otherwise nickel phosphite will be coprecipitated with calcium phosphite.

Accordingly, it is a general object of the present invention to provide an improved process of completely. regenerating a chemical nickel plating solution of the'nickel cation-hypophosphite anion type that involves a greatly minimized number of individual steps.

Another object of the invention is to provide an improved process of removing phosphite anions from a depleted chemical nickel plating solution of the type noted, Without the prior removal of nickel cations from the solution, and without precipitation of the nickel cations in the solution.

Another object of the invention is to provide an improved process of the character noted, wherein the phosphite anions in'the plating solution are precipitated therein a as an alkaline earth phosphite in the presence of nickel cations therein, and without the coprecipitation of nickel phosphite.

, Another object of the invention is to provide an improved process of the character noted, wherein the nickel cations are completely complexed in the solution undergoing treatment, so that the precipitation of an alkaline earth phosphite therein does not efifect the coprecipitation ofvnickel phosphite therein even though the pH of the solution is well above 8.

A further object of. the invention is to provide an improved process of the character noted, that involves the utilization of ammonia as the complexing agent to prevent the coprecipitation of nickel phosphite with the alkaline earth phosphite from the solution undergoing treat- .ment.

vA further object of the invention is to provide an improved process of the character noted, wherein the nickel cations are completely complexed with ammonia and the phosphite anions are precipitated as calcium phosphite.

,A further object of the invention is to provide an improved process of the character noted, wherein the complete complexing of the nickel cations is achieved in a pressurized treatment system employing gaseous ammonia.

, anion type that is simple and economical to carry out.

Further features of the invention pertain to the particular arrangement of the steps of the process, whereby the above-outlined and additional operating features thereof are attained.

, A The invention, both as to its organization and principle of operation, together with further objects and advantages thereof, will best be understood by reference to the I following specification taken in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic illustration of the steps involved in the complete regeneration of a chemical nickel plating solution of the nickel cation-hypophosphite anion type, in accordance with the process of the present invention;

Fig. 2 is a diagrammatic illustration of the steps involved in a modified form of the present process; and

Fig. 3 is a diagrammatic illustration of a continuous i nickel plating system in which the plating solution mentioned may be employed.

The present invention is predicated upon the discovery that in a depleted aqueous chemical nickel plating solution of the nickel cation-hydrophosphite anion type, the undesirable phosphite anions may be selectively precipitated in ammonia, or a suitable ammonium salt, and the required alkaline earth cations are supplied to the depeleted plating solution by the addition of the corresponding hydroxide. In any case, the required ammonia is provided in the depleted plating solution, so as completely to complex all of the nickel cations therein, prior to the calcium hydroxide addition for the purpose of precipitating the phosphite as calcium phosphite.

For example, when the plating solution is initially composed employing nickel sulfate and sodium hypophosphite, calcium hydroxide may be advantageously employed, together with ammonium hydroxide. In this case, sodium sulfate is first stripped from the depleted plating solution by crystallization at low temperature and filtration, and then an ammoniacal solution is produced of the resulting solution in which all of the nickel cations therein are in the form of a nickel-ammonia complex, and raising the pH thereof somewhat above 8, and then calcium hydroxide is added to the ammoniacal solution so as to effect the precipitation therein of calcium phosphite, without the co-precipitation of calcium hypophosphite or any nickel compound. After separation of the calcium phosphite, the resulting solution is treated to break the nickel-ammonia complex, with the evolution of ammonia gas; and thereafter the resulting solution is reconstituted to provide a regenerated chemical nickel plating solution of desired composition.

Referring now to Fig. 1, a depleted aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type derived from a continuous plating system may essentially comprise:

NiSO, m./l 0.08

NaH PO m./l 0.224 Na SO -m./l 0.65 H3PO3 m./l Lactic acid m./l 0.3 Propionic acid m./l 0.03 pH 4.5 to 4.7

In accordance with the present process, this depleted plating solution is introduced into a tank 10 and cooled therein by an associated cooling coil 11, while being agitated, to a temperature in the range 0 C. to 5 C., whereby sodium sulfate is crystallized out therein. The resulting suspension is delivered to an associated filter 12, whereby the sodium sulfate is removed therefrom, and the resulting filtrate is delivered to an associated tank 13. Into the tank 13, there is added first ammonium hydroxide, and then calcium hydroxide, in order to supply ammonia and Ca++, so as to increase the pH above about 8 and to precipitate calcium phosphite, without any substantial precipitation of calcium hypophosphite or any nickel salt. Now, of course, it will be understood that i all of the nickel cations in the solution in the tank 13 are the 'presence of the desirable nickel cations and hypophosphite anions, without the co-precipitation of either thenickel cations or the hypophosphite anions, when the ,mckel cations are completely complexed, during the precipitation of an alkaline earth phosphite in the plating solution. In accordance with the arrangement, the required ammonia is supplied to the depleted plating solution'by"'the addition of ammonium hydroxide, gaseous completely complexed, so that they are not co-precipitated as nickel hydroxide or nickel phosphite. In this step, the calcium hydroxideaddition should normally comprise the stoichiometric amount of calcium cations to effect precipitation of all of the phosphite anions, while the ammonium hydroxide addition should normally comprise several times the stoichiometric amount of ammonia, so as positively to insure that all of the nickel cations in the solution are in the nickel-ammonia complex.

The resulting suspension is delivered to an associated filter 14, whereby the calcium phosphite is separated therefrom, and the resulting filtrate is delivered to a closed tank 15 via a conduit including a valve 16. In the tank 15, the solution is heated to a temperature of about 50 C., while being subjected to a subatmospheric pressure by a pump 17 connected to the tank 15, whereby the nickel-ammonia complex is broken, with the liberation of gaseous ammonia that is discharged to the exterior. The solution is then delivered from the tank 15 via a conduit including a valve 18 to a tank 19. In carrying out the process the valve 16 is closed after a quantity of thefiltrate is delivered into the tank15, ancl substantially. the: composition of the initially formulatedsolution and is returned to the continuous plating system for further plating use; and specifically,- the composition of the regeneratedplating solution may be as follows:

In the foregoingprocess of regenerating the depleted plating solution, it will be appreciated that the complete complexingof the nickel cations in the tank 13, underthese'controlled conditions, accommodates precipitationof calcium phosphite, without any substantial precipitation of calcium hypophosphite or any nickel salt. Subsequently,,. following the removal of the calcium. phosphite,,the-nickel=ammonia complex is boken in thetank 15,,by the combination of the heating and: the subatmospheric pressure; whereby the liberated ammonia gasis discharged to the exterior. Also,itis pointed out that, whenthe sodium sulfate is crystallized out,.it carries therewith from 46% to- 67%, by weight, of water of crystallization, and when the calcium phosphite I is precipitated,-

it carries therewith 18%., by weight, of water of crystallization; whereby the processactually effects a. concentration of the depleted solution, notwithstanding the utilization of the aqueous slurry in the tank'13.

The. foregoing; regeneration procedure will be bestillustrated from the following example, wherein and aqueous chemical nickel plating; solution of the nickel cation-hypophosphite anion type was composed having a volume of 36 liters and having the following composition:.

NiSOl; m /l 0.08 NaH PO m /1' 0.224 Lactic acid m /l. 0.30 Propionic acid m./l.. 0.03 pH (adjusted with NaOH) 4.5 to 4.7

This plating solution wasz employed in the continuous;

G./l. Ni++ 4.4 N'aHgPO 24.8. Na HPO' 131.7 Ca++ Trace H 80 32 This depletedplating solution was first subjected to the previously,- described treatmentv in the tank 10. of Fig. 1, whereby the sodium sulfate was crystallized out and. subsequently removedin the filter 12. In the tank 13 (which wasopen. to the atmosphere in this run) there were added to the filtrate first 3.2' m./l. of NH (derived from 7.2

liters of aqueous NH OH solution) and then the slurry, containing. 1.5 m./l. of Ca(.OH) In the treated solution, there was. precipitated calcium phosphite; andthe calcium phosphite was removed by the filter 14. Thereafter, thefiltrate was treated in the tank 15, and theresulting solution was delivered to thetank19. A sample of this'resulting solution was analyzed and was found to contain the following components:

G./l. Ni++ 3 .4 NaH PO 16.7 Na HPO 3 3 .7 Ca++ None H 27 Accordingly, in this salvaged filtrate 77% of the desirable nickel cations were saved, theloss being substantiallyentirely due to lack of complete complexing of the Ni++ in the open tank 13 in this run; and substantially 74% of the undesirable phosphite anions were removed bythe calcium phosphite precipitation. Furthermore, in the calcium phosphite precipitation step, the molar ratio between the-NH and Ni++, in this example, was 40, which isequivalent to 670% ofthe amount of NH3 required theoretically to complex of the nickel cations in the solution, the great excess of NH being employed' in order absolutely to guarantee complete complexing of all of the nickel cations in'the solution during the precipitation of the calcium phosphite.

The salvaged filtrate was delivered to the tank1'6and was reconstituted by the addition of the aqueous makeup solutions, andthe resulting regenerated plating solution having'substantially the: initial composition setforth' was returned to the continuous plating" system for: further use; and bright; smooth nickel coatings were produced on the work-pieces therewith that were in every respect identical to the coatings produced uponthe'original work pieces with the initially composed plating solution;

Referring now to Fig.2, a modified'form' of theprocess is illustrated which is carried out in a pressurized system including a reaction tank 20 that is provided with a cooling coil 21 together with an agitator 22. The reaction tank 20 is connected to a pressure filter 23 that, in turn, is connectedto' a recovery tank 24. In turn, therecovery tank 24' is connected by a conduit 25 to the inlet ofan associated compressor 26, the' outlet of the compressor 26 being connected by a conduit 27' tothe reaction tank 20. Also the system comprises a tank 31 in which the depleted plating solution is stored, and a tank 32 in which an aqueous solution of calcium hydroxide is stored, as well as a bottle'or tank' 33 containing ammonia gas under pressure; The tank 31 is connected to the reaction tank 20 bya' conduit 34 in which there is arranged a pump 35; and the'tank 32-is connected to the reaction tank 20 by a conduit 36 in which there is arranged a pump 37-. The pressure bottle 33 is connected to the reaction tank 20 by a conduit 38 in which a valve 39 is arranged. Fur thermore; the-recovery tank 24 is provided with an outlet conduit41, including a valve 42; which outlet conduit 41" communicates with a regeneration tank 43 provided with an agitator 44.

In this arrangement, the depleted plating solution is pumped from the storage tank 31 into the reaction tank 20by the'associated pump 35, and likewise the aqueous solution of calcium hydroxide is pumped from'the tank 32 into the reaction tank 20 by the pump 37. Also the ammonia gas contained in the pressure bottle 33 is admitted into the reaction tank 20 by control of the valve 39. In this case, the ammonia gas admitted into the reaction tank 20 brings about the formation of thenickelammonia complex in the treated solution, with the small resultingheatingghowever, cooling of the solution undergoing the reacticn is effected by the cooling coil 21'; whereby the t'emperature'ofthe reacted solution is maintained within the general range 0 C. to 5 C. In this case, the ammonia gas is first admitted into the tank 20,

and then the slurry is pumped thereinto so that the calcium phosphite is precipitated concurrently with the crystallizing out of the sodium sulfate; whereby in the pressure filter 23, both the calcium phosphite precipitate and the sodium sulfate crystals are removed and the resulting filtrate is delivered to the recovery tank 24. In this arrangement, the compressor 26 exerts a suction upon the filtrate in the recovery tank 24 in order to insure the removal of gaseous ammonia therefrom and complete breaking of the nickel-ammonia complex. The filtrate is delivered from the recovery tank 24 into the regeneration tank 42; whereby the addition of the'aqueous makeup solutions thereto restores the filtrate to produce the regenerated plating solution of the desired composition in the manner previously explained.

This arrangement of the steps of the present process is very advantageous, as there is substantially no loss of gaseous ammonia from the system and complete complexing of the nickel in the solution undergoing treatment in the reaction tank 20 can be readily insured by maintaining the required pressure head of ammonia gas thereover; which can be accomplished in a ready manner by operation of the compressor 26 and by the control of the valve 39. In passing, it is noted that the ammonia in the bottle 33 is normally in the liquid state and is flashed into the gaseous state at the valve 39 incident to opening thereof.

Referring now to Fig. 3, a conventional continuous chemical nickel plating system is diagrammatically illustrated as comprising a regeneration tank 51, a storage tank 52, a heater 53, a plating tank 54 and a cooler 55, arranged in tandem relation in the order named, together with a pump 56 and a filter 57 arranged in series relation between the storage tank 52 and the heater 53, and a pump 58arranged between the plating tank 54 and the cooler 55.

In the operation of the continuous plating system, the plating solution is regenerated in the regeneration tank 51 (which may correspond in fact to the tank 19 of Fig. 1 or the tank 43 of Fig. 2), and while the plating solution is cool and at a temperature of about 60 C. From the regeneration tank 51, the plating solution is delivered to the storage tank 52 from which it is pumped by the pump 56 through the filter 57 and thence through the heater 53 and delivered to the plating tank 54. In the heater 53, the plating solution is heated to an effective plating temperature in the general range 85 C. to 95 C. From the plating tank 54, the plating solution is pumped by the pump 58 through the cooler 55 and returned to the regeneration tank 51. In the cooler 55, the plating solution is cooled so that the temperature thereof is returned substantially back to about 60 0., prior to the return of the plating solution to the regeneration tank 51. Of course, the work-pieces to be plated are immersed in the plating solution in the plating tank 54 in the usual manner; which work-pieces must necessarily have a catalytic surface so that the plating reaction may proceed. In this connection, it is mentioned that the catalytic elements are cobalt, nickel, palladium, rhodium and ruthenium. However, a large group of other elements can be rendered catalytic either by displacement or by galvanic initiation in the plating solution, so that the autocatalytic plating reaction may proceed. This group of elements includes: aluminum, carbon, copper, iron, manganese, titanium and uranium (as well as silver and gold), and the various alloys thereof. Also insulators can be satisfactorily nickel plated when the surfaces thereof are suitably activated with one of the catalytic elements named.

In the continuous chemical nickel plating system, a plating solution that has been regenerated in accordance with the present process is equally efiective as an initiallycomposed plating solution in the production of bright, smooth coatings upon the work-pieces, that are intimately bonded thereto, and with a high plating rate. Specifically, in the present example, the plating rate is normally in the range 0.9 to 1.0 mil/hour of nickel plating upon the work-pieces. v

In applying the present process of regeneration to the continuous plating system, the whole body of plating solution may be regenerated after several passes thereof through the system, or a fractional part thereof may be by-passed continuously from the cooler 55 to the regeneration equipment, followed by the present treatment and then the return thereof to the regeneration tank 51.

In the foregoing description of the present process, the regeneration of the depleted plating solution was set forth in conjunction with the removal of calcium phosphite utilizing calcium hydroxide as the precipitating agent, and this alkaline earth hydroxide is preferred as a matter of simplicity and economy. However, other alkaline earth hydroxides may be employed to precipitate the corresponding alkaline earth phosphites, when the plating solution is initially composed with a nickel salt, other than nickel sulfate. For example, the plating solution may be initially composed utilizing nickel chloride and sodium hypophosphite; whereby in this case, the alkaline earth hydroxide may be barium hydroxide, strontium hydroxide, or calcium hydroxide.

The procedure utilizing the other alkaline earth hydroxides is identical to that previously described, as it will be understood that it is the complexing of the nickel cations that prevents the precipitation of the various nickel salts. Also, it is mentioned that the various alkaline earth hydroxides are substantially equally effective to bring about the precipitation of the corresponding alkaline earth phosphite without the precipitation of the corresponding alkaline earth hypophosphites.

It is reiterated that when the bath is initially composed with nickel sulfate, then the regeneration must take place with calcium hydroxide, since it will be immediately apparent that the utilization of barium or strontium hydroxides would be primarily effective to bring about the precipitation of the corresponding barium or strontium sulfates and secondarily effective to bring about the precipitation of the corresponding barium or strontium phosphites. In other words, barium sulfate is far less soluble than barium phosphite, and strontium sulfate is far less soluble than strontium phosphite. However, this is not true of other barium salts (barium chloride) and of other strontium salts (strontium chloride). On the other hand, calcium is unique as the sulfate thereof is relatively soluble and so is the chloride; whereby the regeneration procedure using calciumhydroxide has universal application to these plating solutions.

Another consideration is of importance in the regeneration of these plating solutions, as a practical matter, in that it is highly desirable to prevent the introduction of anions that are foreign to those already present thereini While the description has proceeded in terms of the utilization of alkaline earth hydroxides, the corresponding alkaline earth oxides and carbonates are equally effective.

In view of the foregoing, it is apparent that there has been provided an improved process for regenerating a depleted aqueous chemical nickel plating solution of the nickel cation-hypophosphite anion type, wherein the desirable nickel cations and hypophosphite anions are maintained in the solution, while the undesirable phosphite anions are removed therefrom; whereby the treated solution comprises an aqueous and appropriate basis for the reconstitution of a chemical nickel plating solution having substantially the initially formulated composition.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will'be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What isclaimed is:

nickel cations and hypophosphite anions. andundesirable phosphite anions, comprising treating the depleted plating solution to produce an ammoniacal solution thereof inwhich all of the nickel cations therein are in thenickelammonia complex, thenadding to the ammoniacal. solution alkaline earth hydroxide so as to precipitate therein alkaline earth-phosphite without'precipitating therein any substantial amounts of alkaline earth'hypophosphite or of any nickel: compound, said alkaline earth hydroxide ad' dition to said ammoniacal solution being sufiicient to effect theremoval therefrom of a substantial proportion of the phosphite anions therein, removingthe precipitated alkaline earth phosphite from the resulting solution, then removing ammonia from the resulting solution to break the nickel-ammonia complex therein, and then adding to the resulting solution the required nickel cations and hypophospite anions. and hydrogen ions to produce a plating solution of desired composition.

2. The process of regenerating a depleted aqueous:

chemical nickel plating solution containing desirable nickel cations and hypophosphite anions and undesirable phosphite anions, comprising treating the depleted plating solution with ammonia under pressure so as to produce an ammoniacal solution thereof in which all of the nickel cations therein are in the nickel-ammonia complex, then adding to the ammoniacal solution while it is under ammonia pressure alkaline earth hydroxide so as to precipitate therein alkaline earth phosphite without precipitating therein any substantial amounts of alkaline earth hypophosphite or of any nickel compound, said alkaline earth hydroxide addition to said ammoniacal solution being sufiicient to effect the removal therefrom of a substantial proportion of the phosphite anions therein, removing the precipitated alkaline earth phosphite from the treated solution While it is under ammonia pressure, then relieving the ammonia pressure and removing ammonia from the resulting solution to break the nickelammonia complex therein, and then adding to the re sulting solution the required nickel cations and hypophosphite anions and hydrogen ions to produce a plating solution of desired composition.

3. The process of regenerating a depleted aqueous chemical nickel plating solution containing desirable nickel cations and hypophosphite anions and undesirable phos phite anions, comprising adding to the depleted solution sufficient ammonium hydroxide completely to complex all of the nickel cations therein, then treating the resulting solution With alkaline earth hydroxide so as to precipitate therein alkaline earth phosphite Without precipitating therein any substantial amounts of alkaline earth hypophosphite or of any nickel compound, said alkaline earth hydroxide addition to said ammoniacal solution being sufficient to effect the removal therefrom of a substantial proportion of the phosphite anions therein, removing the precipitated alkaline earth phospite from the treated solution, then removing ammonia from the resulting solution to break the nickel-ammonia complex therein, and then adding to the resulting solution the required nickel cations and hypophosphite anions and hydrogen ions to produce a plating solution of desired composition.

4. The process of regenerating a depleted aqueous 7 chemical nickel plating solution containing desirable nickel cations and hypophosphite anions and undesirable phosphite anions, comprising adding to the depleted solution sufiicient ammonium hydroxide completely to complex all of the nickel cations therein, then treating the resulting solution with calcium hydroxide so as to precipitate therein calcium phosphite Without precipitating therein any substantial amounts of calcium hypophosphite or of any nickel compound, said calcium hydroxide addition to said ammoniacal solution being suflicient to effect the removal therefrom of a substantial proportion of the phosphitev anions. therein, removing: the precipitated. cal-- cium phosphite: from the: treated. solution, then removing ammonia from the resulting;soli1tion. to breaktthe nickelammonia complex therein, andthen adding: to the resulting solution the requiredi nickel. cations and hypophosphite anions. and: hydrogen ions to-produce a plating;

solution of;desired'composition.v

5; The process: of; regenerating a depleted aqueous chemical nickel platingtsolutioln containing desirable nickel cations and hypophosphite anionsand undesirable sodium.

cations and: phosphite anions" and sulfate anions, comprising cooling the. depleted solution to a temperature atleast asslow as 5 C. so: as to crystallize outsodiumsulfate therein, removing the: sodium sulfate from the cooled solution, treating theresulting solution to produce an ammoniacal solution thereof in. which all of thenickel cations. thereinare in.the nickel-ammonia complex, then adding to. the'ammoniacal'solution alkaline earth hydroxide: so. as to precipitate therein alkalineearth' phosphitevvithout. precipitating. therein; any substantial amounts of alkaline-earthhypophosphite'or ofany nickel compound, said alkaline earth hydroxide: addition. to said ammoniacal solution being sufiicient to eflect the removal therefrom of a substantial proportion of the phosphite anions therein, removing the precipitated alkaline earth phosphite from the resulting solution, then removing ammonia from the resulting solution to break the nickel-ammonia complex therein, and then adding to the resulting solution the required amounts of nickel sulfate and sodium hypophosphite and hydrogen ions to produce a plating solution of desired composition. W

6. The process of regenerating a depleted aqueous chemical nickel plating solution containing desirable nickel cations and hypophosphite anions and undesirable sodium cations and phosphite anions and sulfate anions, comprising cooling the depleted solution to a temperature at least as low as 5 C. so as to crystallize out sodium sulfate therein, removing the sodium sulfate from the cooled solution, treating the resulting solution to produce an ammoniacal solution thereof in which all of the nickel cations therein are in the nickel-ammonia complex, then adding to the ammoniacal solution calcium hydroxide so as to precipitate therein calcium phosphite Without precipitating therein any substantial amounts of calcium hypophosphite or of any nickel compound, said calcium hydroxide addition to said ammoniacal solution being sufilcient to effect the removal therefrom of a substantial proportion of the phosphite anions therein, removing the precipitated calcium phosphite from the resulting solution, then removing ammonia from the resulting solution to break the nickel-ammonia complex therein, and then adding to the resulting solution the required amounts of nickel sulfate and sodium hypophosphite and hydrogen ions to produce a plating solution of desired composition.

7. The process of regenerating a depleted aqueous chemical nickel plating solution containing desirable nickel cations and hypophosphite anions and undesirable sodium cations and phosphite anions and sulfate anions, comprising cooling the depleted plating solution to a temperature at least as low as 5 C. so as to crystallize out sodium sulfate therein, removing the sodium sulfate from the cooled solution, adding to the resulting solution sufficient ammonium hydroxide completely to complex all of the nickel cations therein, then treating the resulting solution with calcium hydroxide so as to precipitate therein calcium phosphite Without precipitating therein any substantial amounts of calcium hypophosphite or of any nickel compound, said calcium hydroxide addition to said ammoniacal solution being sufiicient to eifect the removal therefrom of a substantial proportion of the phosphite anions therein, removing the precipitated calcium phosphite from the treated solution, then removing ammonia from the resulting solution to break up nickel-ammonia complex therein, and then adding to the resulting solu tion the required amounts of nickel sulfate and sodium hypophosphite and hydrogen ions to produce a plating solution of desired composition.

8. The process of regenerating a depleted aqueous chemical nickel plating solution containing desirable nickel cations and hypophosphite anions and undesirable sodium cations and phosphite anions and sulfate anions, comprising cooling the depleted plating solution to a temperature in the range C. to C. while subjecting the same to a head pressure of ammonia and while adding thereto calcium hydroxide so as to crystallize out therein sodium sulfate and so as to produce an ammoniacal solution thereof in which all of the nickel cations therein are in the nickel-ammonia complex and so as to precipitate therein calcium phosphite without precipitating therein any substantial amounts of calcium hypophosphite or of any nickel compound, said calcium hydroxide addition to said ammoniacal solution being suflicient to effect the removal therefrom of a substantial proportion of the phosphite anions therein, removing simultaneously the sodium sulfate and the calcium phos-' phite from the cooled solution while it is under ammonia hypophosphite and hydrogen ions to produce a plating solution of desired composition.

9. The process set forth in claim 1, wherein said alkaline earth hydroxide is calcium hydroxide.

10. The process set forth in claim 1, wherein said alkaline earth hydroxide is barium hydroxide.

l l. alkaline earth hydroxide is strontium hydroxide.

References Cited in the file of this patent Theoretical Chemistry, Longmans, Green & Co., New York, 1928, vol. 8, pages 879 and 914-915.

he process set forth in claim 1, wherein said 

1. THE PROCESS OF REGENERATING A DEPLETED AQUEOUS CHEMICAL NICKEL PLATING SOLUTION CONTAINING DESIRABLE NICKEL CATIONS AND HYPOPHOSPHITE ANIONS AND UNDESIRABLE PHOSPHITE ANIONS, COMPRISING TREATING THE DEPLETE PLATING SOLUTION TO PRODUCE AN AMMONIACAL SOLUTION THEREOF IN WHICH ALL OF THE NICKEL CATIONS THEREIN ARE IN THE NICKELAMMONIA COMPLEX, THEN ADDING TO THE AMMONIACAL SOLUTION ALKALINE EARTH HYDRROXIDE SO AS TO PRECIPITATE THEREIN ALKALINE EARTH PHOSPHITE WITHOUT PRECIPITATING THEREIN ANY SUBSTANTIAL AMOUNTS OF ALKALINE EARTH HYPOPHOSPHITE OR OF ANY NICKEL COMPOUND, SAID ALKALINE EARTH HYDROXIDE ADDITION TO SAID AMMONIACAL SOLUTION BEING SUFFICIENT TO EFFECT THE REMOVAL THEREFROM OF A SUBSTANTIAL PROPORTION OF THE PHOSPHITE ANIONS THEREIN, REMOVING THE PRECIPITATED ALKALINE EARTH PHOSPHITE FROM THE RESULTING SOLUTION, THEN REMOVING AMMONIA FROM THE RESULTING SOLUTION TO BREAK THE NICKEL-AMMONIA COMPLEX THEREIN, AND THEN ADDING TO THE RESULTING SOLUTION THE REQUIRED NICKEL CATIONS AND HYPOPHOSPITE ANIONS AND HYDROGEN IONS TO PRODUCE A PLATING SOLUTION OF DESIRED COMPOSITION. 